74 



SCIENCE. 



[Vol. XX. No. 496 



combination whatever of natural bodies to derive an un- 

 limited amount of meclianical force [energy], or on the as- 

 sumption that all actions in nature can be ultimately referred 

 to attractive or repulsive forces, the intensity of which de- 

 pends solely upon the distances between the points by which 

 the forces are exerted/' He showed also that it was imma- 

 terial which of these maxims was assumed, as the other could 

 be at once obtained from it. How by the aid of either of 

 these hypotheses we pass from the equation given above to 

 the law of the conservation of energy is of course well known. 

 The point to which it seems necessary to draw attention is 

 that some hypothesis is required, and that either of these is 

 sufficient for the purpose. 



As the second of Helmholtz's maxims is simply an exten- 

 sion of the third law of motion, and as Newton's three laws 

 have obtained such wide usage, it would seem to be desirable 

 to adopt the second maxim as a fourth law of motion. Were 

 we to select the first maxim, it would be necessary to re-cast 

 our fundamental hypotheses altogether.^ Possibly it might 

 be advantageous to take this course, to make, as Tait^ sug- 

 gests, the laws of the conservation and the transformation 

 of energy our fundamental hypotheses, and to banish the 

 conception of force to the limbo of once useful things. But 

 if Newton's laws are to be retained, they should be supple- 

 mented by the second of Helmholtz's assumptions. 



It is at once obvious that this fourth law will, like the 

 third, be independent of points of reference; and it follows 

 that the law of the conservation of energy will hold rela- 

 tively to all points by reference to which the second law 

 holds. This conclusion is inconsistent with Newcomb's 

 assertion^ that this law '' assumes that we refer the motions 

 of all the bodies whose energy is considered to some foreign 

 body of infinite mass, from which emanate the forces which 

 give motion to the system." According to the above, this 

 law may of course be expressed relatively to a particle of 

 infinite mass, and, if thus expressed, the forces which give 

 motion to the system may be supposed to emanate from that 

 particle. But it may also be expressed relatively either to a 

 particle of finite mass free from the action of force, or to 

 the centi'e of mass of the system itself whose energy is con- 

 served. 



4. Reduction of the Laws of Motion. 



Finally, the four laws of motion may obviously be re- 

 duced to two. The first has already been seen to be a par- 

 ticular case of the second. The third is involved in the 

 fourth; for when it is asserted that natural forces are attrac- 

 tions or repulsions, it is implied that their action and reac- 

 tion are in opposite directions, and when it is asserted that 

 they may be expressed as functions of the distances of the 

 particles between which they act, it is implied that their action 

 and reaction are equal. The four laws thus reduce to two, 

 which may be enunciated somewhat as follows: — 



The Law of Force. — Relatively to any particle free from 

 the action of force, the acceleration produced in another 

 particle by a force is proportional to the force and has the 

 same direction. 



The Law of Stress. — Natural forces may be considered 

 to be attractions or repulsions whose magnitudes vary 

 solely with the distances of the particles between which 

 they act. 



* Many writers illogically select the first maxim as a fourth law. See Pro- 

 fesBor Johnson's paper cited above ; also my Kinematics and Dynamics, 

 5 436 



' Ency. Brit., 9th Kd., Art. Mechanics, 5 291. 



3 I'hil. Mag., Ser. 5, Vol xxvil. (1889), p. 116. 



THE GREAT LAKE BASINS. 



BT P. J. PAHNSWORTH. 



The problem of the origin of the Great Lakes has for a 

 long time engaged the attention of the scientists, who have 

 come to a variety of conclusions, none of them very satis- 

 factory. Subsidence, ice action, glacial scooping, and Presi- 

 dent Chamberlin's theory that they were hollows made by 

 accumulating ice bending down the earth's crust. 



An article in Science of June 3 presents a more plausible 

 theory, that they are vallies of erosion, made by some great 

 river, giving as evidence the map of Dr. Spencer, pointing- 

 out the discoveries and probable deep pre-glacial channels: 

 leading into the St. Lawrence and the Atlantic. Professor 

 Spencer, in his paper on High Continental Elevations, read 

 at the Scientific Association at Toronto, 1889, sums up by- 

 saying, " The lake basins are merely closed-up portions of 

 the ancient St. Lawrence valley and its tributaries." " The 

 lake basins are all excavated out of Palaeozoic rocks except 

 a part of that of Lake Superior." 



If we go back in geologic history to Azoic times we findi 

 that the first emergence of the continent was the V shaped 

 land around Hudson's Bay, an open sea below it. Next, aa 

 emergence of a point below the V and a line of height ex- 

 tending along the lower side of what we call the river and 

 gulf of St. Lawrence. A sea or strait extended round the- 

 primitive land from the Atlantic to the Arctic Ocean on the 

 north-west. After the elevation of the trough at the north- 

 west, an inland sea was left covering Superior, Michigan,. 

 Huron, and Ontario, leading into the St. Lawrence Gulf. 

 In time there was elevation and subsidence and flexion of 

 strata, as pointed out by Professor Spencer, and the great 

 basins were left as interior seas. There was a large water- 

 shed to the north that compelled an overflow, that made 

 its way in the deep channels that have been discovered, 

 at some time out of Ontario, across New York, then, if tliere^ 

 was continental elevation, making the deep channels down 

 the valley of the St. Lawrence and far out into the Gulf. 

 Lake Champlain was a pool in a fissure of the Azoac world,, 

 that was connected with the open channel in the Archean 

 land. 



The ice period so obstructed the old outlet that when it. 

 was melting, the superfluous waters of the great basins were 

 poured into the Gulf of Mexico through the Illinois and 

 Wabash rivers. When the ice disappeared, the old outlet had 

 become obstructed by flexions of strata and mountains of 

 drift. It is evident that Lake Michigan had a channel 

 through Georgian Bay, and thence into Ontario. It is not. 

 yet apparent where the deep channel for the waters of Su- 

 perior came in, or that it had any such. It has an insignifi- 

 cant but sufficient outlet through the St. Mary's River. 

 Michigan and Huron reach Ontario over the St. Clair flats- 

 and through the shallow trough that holds Lake Erie, which- 

 probably is of post-glacial age, and then into Ontario down 

 the hill that is being cut back by the falls of Niagara. 



The great lakes were deep seas before the world was cold 

 enough for ice, and were great basins b3fore glaciers were 

 possible. 



One could hardly conceive how glacial ploughing coming 

 from the north or north-east could make chasms at such an- 

 gles to each other. In regard to cut of channels of erosion,, 

 it would require a river from the south-west and north-west,, 

 from Michigan and Superior, of such magnitude that great 

 valleys or traces of them would be left. Lake Superior is- 

 360 miles long and 150 miles wide in some places, with a. 



